The invention relates to a process to produce dialkyl and diaryl ethers. The disclosed process includes the reaction of carbon dioxide with a metal alcoholate, also known as a metal alkoxide, to form the dialkyl and diaryl ethers. A specific example of dimethyl ether (DME) production is disclosed.
Dimethyl ether (DME) is a clean burning fuel that can be used in diesel engines or as an additive to diesel fuel. The cetane number is slightly higher than diesel and can be stored and transported like liquid petroleum gas (LPG). It liquefies at −25° C. or about 6 atmospheres. Burning DME in diesel engines results in a lower NOx with no SOx.
Dimethyl ether can be substituted for liquefied petroleum gas (LPG), as a blended fuel, or reformed into hydrogen for fuel cells. DME has been increasingly used as a propellant in aerosol formulations to replace chlorofuorocarbons. DME is becoming a promising building block in the fuel and petrochemical industry.
One conventional production method of DME derives from synthesis gas (hydrogen and carbon monoxide) reacted over a mixed catalyst reactor at high temperature and pressure. Conversion rates per pass over the catalyst are as low as 18 to 50 percent. The reaction formulas and reaction heat concerning DME synthesis are as follows:3CO+3H2→CH3OCH3+CO2+246.0 kJ/DME-mol  (1)2CO+4H2→CH3OCH3+H2O+205.0 kJ/DME-mol  (2)2CO+4H2→2CH3OH+181.6 kJ/DME-mol  (3)2CH3OH→CH3OCH3+H2O+23.4 kJ/DME-mol  (4)CO+H2O→CO2+H2+41.0 kJ/DME-mol  (5)
Reaction (1) synthesizes DME from synthesis gas (H2, CO) in three steps: methanol synthesis reaction (3), dehydration reaction (4), and shift reaction (5). When the shift reaction is slow, reactions (3) and (4) are combined into reaction (2). Overall the reaction is exothermic and the reaction heat at methanol synthesis step is dominant.
Another known production method of DME is the catalytic dehydration of methanol according to reaction (4) above. One such process is carried out in an adiabatic reactor with an inlet methanol temperature above 250° C.
It will be appreciated that there is a need in the art for a process for producing DME and more generally a process for producing dialkyl and diaryl ethers which does not require high temperature, pressure, or solid catalysts.